Steps to reproduce the issue

A new fresh Joomla 4 installation with PHP 7.4.
Set the administrator's default language other than English (for example Italian).
Create a new Administrator User and set "Receive System Emails" on YES.

Expected result

The user should be receive this Email, with Sitename, Username and Password:

Hello Marc,

You have been added as a User to Sitename by an Administrator.

This email has your username and password to log in to https://www.sitename

Username: Marc
Password: 123456789

Actual result

For example, with Italian default Administrator Language, Login Data are shown with %s:

Salve %s,

sei stato aggiunto come Utente sul sito %s da un Amministratore.

Questa email contiene i tuoi nome utente e password per accedere a %s

Nome utente: %s
Password: %s

Non rispondere a questo messaggio in quanto generato automaticamente e solo a scopo informativo.

System information (as much as possible)

PHP Built On Linux dalin.dnshigh.com
Database Type mysql
Database Version 5.7.35-log
Database Collation utf8_general_ci
Database Connection Collation utf8mb4_general_ci
Database Connection Encryption None
Database Server Supports Connection Encryption Yes
PHP Version 7.4.23
Web Server Apache
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 4.0.3 Stable

Additional comments

It looks like a Language Association Issue...